DSpace collection: 期刊論文

Thermal annealing and grain boundary effects on ferromagnetism in Y(2)O(3):Co diluted magnetic oxide nanocrystals

Tue, 27 Mar 2012 10:13:31 GMT

title: Thermal annealing and grain boundary effects on ferromagnetism in Y(2)O(3):Co diluted magnetic oxide nanocrystals abstract: Structures and magnetic properties of Y(2)O(3):Co nanocrystals were investigated using high resolution transmission electron microscopy, x-ray diffraction, x-ray absorption fine structures, and superconducting quantum interference device. Cobalt atoms were found to be driven by thermal annealing from interstitial locations inside the Y(2)O(3) nanoparticles toward particle surface, where increased O vacancies surrounding Co atoms led to increased saturation magnetization. Our results strongly support a bound magnetic polaron model for ferromagnetism in diluted magnetic oxides mostly due to magnetic dopants located on the grain boundaries. (C) 2011 American Institute of Physics. [doi:10.1063/1.3544059]

Synthesis of quinoxaline-benzoxale conjugates and mesomorphic properties

Tue, 27 Mar 2012 10:13:28 GMT

title: Synthesis of quinoxaline-benzoxale conjugates and mesomorphic properties abstract: A new series of non-discotic heterocyclic compounds 1a-e derived from quinoxaline was prepared and their mesomorphic properties investigated. The crystal and molecular structures of nonmesogenic 2,3-bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid 4-[(4-butoxy2-hydroxyphenylimino)methyl] phenyl ester 2a (n=4, m=12) were determined by means of X-ray structural analysis. It crystallizes in a monoclinic space group P2(1)/c, with a=21.9193(13) angstrom, b=8.3693(4) angstrom, c=30.896(2) angstrom, and Z=4. The molecule was considered as an elongated or tapered triangle. Both inter- and intra-molecular H-bonds were observed in the crystal lattice, which was attributed to the formation of columnar mesophase in compounds 2. The mesomorphic behavior of compounds 1-2 was studied by thermal analysis and polarized optical microscopy. All compounds 1-2 exhibited hexagonal columnar phases (Col(h)), which were also confirmed by powder XRD diffractometer. A N(cell) and R(ar) value equal to 4.74 and 4.34 within a slice of 9.0 angstrom thick were obtained for 1b and 2b, indicating that a more disc-like correlated structure by two molecules lying side-by-side was formed in Col(h) phases. The fluorescent properties of the compounds 1-4 in CH(3)Cl were also examined. (C) 2010 Elsevier Ltd. All rights reserved.

Synthesis of Cu nanoparticles in mesoporous silica SBA-15 functionalized with carboxylic acid groups

Tue, 27 Mar 2012 10:13:24 GMT

title: Synthesis of Cu nanoparticles in mesoporous silica SBA-15 functionalized with carboxylic acid groups abstract: In this study, the mesoporous silica SBA-15 materials containing carboxylic acid groups were used as an effective support to synthesize Cu nanoparticles. Various Cu loading levels from 4% to 13% on SBA-15 catalysts produced an average particle size of 2.8 to 3.1 nm, regardless of the Cu content.

Synthesis and two-photon properties of a multi-polar chromophore based on tetra-quinoxalinylethylene scaffold

Tue, 27 Mar 2012 10:13:20 GMT

title: Synthesis and two-photon properties of a multi-polar chromophore based on tetra-quinoxalinylethylene scaffold abstract: A new multi-branched fluorophore derived from tetra-quinoxalinylethylene as the core with diphenylaminofluorene units incorporated at the peripheral positions has been synthesized via Pd-catalyzed Suzuki coupling and experimentally shown to possess strong solvent effect on its fluorescence emission and lifetime behaviors. The initial characterization also found that this dye molecule exhibits two-photon activities and effective optical power limiting properties in the near-IR region under the irradiation of nanosecond laser pulses. (C) 2011 Elsevier Ltd. All rights reserved.